1. Field of the Invention
The present invention relates generally to three-dimensional measurement apparatus and, more particularly, to a three-dimensional measurement apparatus in which it is possible to use a non-contact type detecting sensor and a probe type detecting sensor, as required, while switching either of them to the other.
2. Description of the Related Art
Probe type three-dimensional measurement apparatus are commonly used to measure dimensions of mechanical components or the like. Such a measurement apparatus is arranged to provide a measure of an object while keeping the probe of a probe type detecting sensor in direct contact with the object.
Such a probe type three-dimensional measurement apparatus which relies upon the related art can be used to measure an object having a mirror plane or dimensions of an object having a definite shape (such as a cube or a column) which requires critical measurement accuracy. Such a conventional probe type three-dimensional measurement apparatus, however, presents the following problems. For example, since it is necessary to compensate for the diameter of the probe with respect to the inclination of each measuring surface of an object, it is difficult to apply such a probe type measurement apparatus to measurement of a three-dimensional free-curved surfaces, that is, the measurement of the shape of an object having three-dimensional free-curved surfaces. There is a risk of damaging or deforming an object during measurement. Also, it is difficult to increase speeds of measurement.
In recent years, non-contact type three-dimensional measurement apparatus have been developed. This type of measurement apparatus typically employs, in place of the probe of the probe type detecting sensor, a light-spot-position detecting sensor which is a non-contact type detecting sensor arranged to measure a distance to an object in a non-contact manner by illuminating the object with a laser beam. In this type of detecting sensor, the laser beam emitted from a light source illuminates the object, and a portion of reflected light is passe through a lens system to reach a detector for detecting the position of the object. If the object is moved toward or away from the laser probe, reflected light reaches a different point on the detector surface, which point differs from the point upon which the reflected light fell prior to the movement of the object. This positional change is subjected to electrical signal processing, whereby a distance to the object is measured. The range in which the positional change can be measured is small, for example 32 mm. Such a non-contact type three-dimensional measurement apparatus is disclosed in Japanese Patent Unexamined Publication No. 60-20530.
The above-described conventional non-contact type three-dimensional measurement apparatus employing the light-spot-position detecting sensor does not involve the aforementioned problems which are presented by the probe type three-dimensional measurement apparatus. Accordingly, it is possible to perform high-speed measurement of the shape of an three-dimensional free-curved-surface object and measurement of the shape of a soft object However, the conventional non-contact type three-dimensional measurement apparatus involves the following problems. That is, the non-contact type apparatus is generally inferior in measurement accuracy to the probe type apparatus because of specific phenomena derived from the reflection of a laser beam. Also, it has been impossible to measure an object having a mirror plane such as a glass plate.